1. Field of the Invention
The present invention relates to biodegradable homopolymer and block copolymer compositions, in particular those containing both phosphite and terephthalate ester linkages in the polymer backbone, which degrade in vivo into non-toxic residues. The copolymers of the invention are particularly useful as essentially non-osteoconductive, non-porous implantable medical devices and drug delivery systems.
2. Description of the Prior Art
Biocompatible polymeric materials have been used extensively in therapeutic drug delivery and medical implant device applications. Sometimes, it is also desirable for such polymers to be, not only biocompatible, but also biodegradable to obviate the need for removing the polymer once its therapeutic value has been exhausted.
Conventional methods of drug delivery, such as frequent periodic dosing, are not ideal in many cases. For example, with highly toxic drugs, frequent conventional dosing can result in high initial drug levels at the time of dosing, often at near-toxic levels, followed by low drug levels between doses that can be below the level of their therapeutic value. However, with controlled drug delivery, drug levels can be more easily maintained at therapeutic, but non-toxic, levels by controlled release in a predictable manner over a longer term.
If a biodegradable medical device is intended for use as a drug delivery or other controlled-release system, using a polymeric carrier is one effective means to deliver the therapeutic agent locally and in a controlled fashion, see Langer et al., xe2x80x9cChemical and Physical Structures of Polymers as Carriers for Controlled Release of Bioactive Agentsxe2x80x9d, J. Macro. Science, Rev. Macro. Chem. Phys., C23:1, 61-126 (1983). As a result, less total drug is required, and toxic side effects can be minimized. Polymers have been used as carriers of therapeutic agents to effect a localized and sustained release. See Leong et al., xe2x80x9cPolymeric Controlled Drug Deliveryxe2x80x9d, Advanced Drug Delivery Reviews, 1:199-233 (1987) and Langer, xe2x80x9cNew Methods of Drug Deliveryxe2x80x9d, Science, 249:1527-33 (1990); and Chien et al., Novel Drug Delivery Systems (1982). Such delivery systems offer the potential of enhanced therapeutic efficacy and reduced overall toxicity.
For a non-biodegradable matrix, the steps leading to release of the therapeutic agent are water diffusion into the matrix, dissolution of the therapeutic agent, and diffusion of the therapeutic agent out through the channels of the matrix. As a consequence, the mean residence time of the therapeutic agent existing in the soluble state is longer for a non-biodegradable matrix than for a biodegradable matrix, for which passage through the channels of the matrix, while it may occur, is no longer required. Since many pharmaceuticals have short half-lives, therapeutic agents can decompose or become inactivated within the non-biodegradable matrix before they are released.
This issue is particularly significant for many bio-macromolecules and smaller polypeptides, since these molecules are generally hydrolytically unstable and have low permeability through a polymer matrix. In fact, in a non-biodegradable matrix, many bio-macromolecules aggregate and precipitate, blocking the channels necessary for diffusion out of the carrier matrix.
These problems are alleviated by using a biodegradable matrix that, in addition to some diffusion release, also allows controlled release of the therapeutic agent by degradation of the polymer matrix. Use of a biodegradable polymer matrix also obviates the need for the polymer to form a highly porous material since the release of the therapeutic agent is no longer soley conditioned upon diffusion through the pores of the polymeric matrix. Examples of classes of synthetic polymers that have been studied as possible biodegradable materials include polyesters (Pitt et al., xe2x80x9cBiodegradable Drug Delivery Systems Based on Alipathic Polyesters: Application to Contraceptives and Narcotic Antago-nistsxe2x80x9d, Controlled Release of Bicactive Materials, 19-44 (Richard Baker ed., 1980); poly(amino acids) and pseudo-poly(amino acids) (Pulapura et al., xe2x80x9cTrends in the Development of Bioresorbable Polymers for Medical Applications,xe2x80x9d J. of Biomaterials Appl., 6:1, 216-50 (1992); polyurethanes (Bruin et al., xe2x80x9cBiodegradable Lysine Diisocyanate-based Poly-(Glycolide-co-xcex5 Caprolactone)-Urethane Network in Artificial Skinxe2x80x9d, Biomaterials, 11:4, 291-95 (1990); polyorthoesters (Heller et al., xe2x80x9cRelease of Norethin-drone from Poly(Ortho Esters)xe2x80x9d, Polymer Engineering Sci., 21:11, 727-31 (1981); and polyanhydrides (Leong et al., xe2x80x9cPolyanhydrides for Controlled Release of Bioactive Agentsxe2x80x9d, Biomaterials, 7:5, 364-71 (1986).
Specific examples of biodegradable materials that are used as medical implant materials are polylactide, polyglycolide, polydioxanone, poly(lactide-co-glycolide), poly(glycolide-co-polydioxanone), polyanhydrides, poly(glycolide-co-trimethylene carbonate), and poly(glycolide-co-caprolactone). Injectable polyphosphazenes have also been described as useful for forming solid biodegradable implants in situ. See, Dunn et al., in U.S. Pat. Nos. 5,340,849; 5,324,519; 5,278,202; and 5,278,201.
Polymers having phosphoester linkages, called poly(phosphates), poly(phosphonates) and poly(phosphites), are known. See Penczek et al., Handbook of Polymer Synthesis, Chapter 17: xe2x80x9cPhosphorus-Containing Polymersxe2x80x9d, 1077-1132 (Hans R. Kricheldorf ed., 1992). The respective structures of each of these three classes of compounds, each having a different side chain connected to the phosphorus atom, is as follows: 
The versatility of these polymers comes from the versatility of the phosphorus atom, which is known for a multiplicity of reactions. Its bonding can involve the 3p orbitals or various 3s-3p hybrids; spd hybrids are also possible because of the accessible d orbitals. Thus, the physico-chemical properties of the poly(phosphoesters) can be readily changed by varying either the R or Rxe2x80x2 group. The biodegradability of the polymer is due primarily to the physiologically labile phosphoester bond in the backbone of the polymer. By manipulating the backbone or the side chain, a wide range of biodegradation rates are attainable. Kadiyala et al., Biomedical Applications of Synthetic Biodegradable Polymers, Chapter 3: xe2x80x9cPoly(phosphoesters): Synthesis, Physicochemical Characterization and Biological Responsexe2x80x9d, 33-57, 34-5 (Jeffrey O. Hollinger ed., 1995). See also copending U.S. patent application Ser. No. 09/053,648 for a discussion of terephthalate poly(phosphate) polymers useful as biodegradable materials.
An additional feature of poly(phosphates) and poly(phosphonates) is the availability of functional side groups. Because phosphorus can be pentavalent, drug molecules or other biologically active substances can be chemically linked to the polymer, as well as physically dissolved in the polymer, prior to shaping the polymer into its final form. For example, drugs with xe2x80x94O-carboxy groups may be coupled to the phosphorus via an ester bond, which is hydrolyzable. The Pxe2x80x94Oxe2x80x94C group in the polymer backbone also lowers the glass transition temperature of the polymer and, importantly, confers solubility in common organic solvents, which is desirable for easy characterization and processing. Kadiyala et al. at page 35.
Poly(phosphite) esters have been known for some time. Specifically, Coover et al., U.S. Pat. No. 3,271,329, discloses the production of polymers from dialkyl or diaryl hydrogen phophites and certain glycols or dihydroxy aromatic hydrocarbons. The resulting high molecular weight polymers were found to be highly flame resistent.
Similarly, Friedman, U.S. Pat. No. 3,422,982, discloses polyphosphites of 2,2-dimethyl-3-hydroxypropyl-2-dimethyl-3-hydroxypropionate. The resulting compounds were found to be remarkably stable toward hydrolysis, heat and light, and were therefore taught to be useful as stabilizers for other polymers.
Kadiyala et al. discloses loading a biodegradable porous material with bone morphogenetic proteins to make a bone graft for large segmental defects. Kadiyala et al. also discloses reacting bis(2-hydroxyethyl) terephthalate with dimethyl phosphite to form the following biodegradable poly(phosphite): 
Lyophilized pellets of a powder of the above polymer, abbreviated xe2x80x9cPPETxe2x80x9d, were implanted subcutaneously in rats to test soft tissue response, and compression molded bone plugs were implanted in rabbits. No inflammatory response was observed. However, the polymer underwent very rapid breakdown, and structural rigidity was lost.
Lo discloses using the above biodegradable poly(phosphite), poly[bis(2-ethoxy)hydrophosphonic terephthalate] (PPET), as a biodegradable macroporous structure attractive for bone graft applications. Bone implant studies are said to suggest good body tolerance of the material. However, no formation of new bone was observed, leaving osteoconductivity speculative, possibly due to the rapid in vivo degradation rate. Hungnan Lo, xe2x80x9cSynthesis of Biodegradable Polymers and Porous Grafts for Orthopedic Applicationsxe2x80x9d (Jan. 27, 1995) (Ph.D. dissertation, The Johns Hopkins University).
However, neither Kadiyala et al. or Lo describes terephthalate poly(phosphites), which do not have a pendant sidechain, specifically as being particularly well-suited for making biodegradable drug delivery systems.
Applicants now have discovered that essentially non-osteoconductive compositions can advantageously comprise:
(a) at least one biologically active substance and
(b) a polymer having the recurring monomeric units shown above in formula I: 
xe2x80x83wherein R is a divalent organic moiety;
x is xe2x89xa71; and
n is 3-7,500,
xe2x80x83where the biodegradable polymer is sufficiently pure to be biocompatible and is capable of forming biocompatible residues upon biodegradation.
In another embodiment, the invention comprises essentially non-osteoconductive medical devices comprising the above-described composition. Preferably, the device of the invention is non-porous and adapted for implantation or injection into the body of an animal.
In a still further embodiment of the invention, a method is provided for the controlled release of a biologically active substance comprising the steps of:
(a) combining the biologically active substance with an essentially non-osteoconductive biodegradable terephthalate polymer having the recurring monomeric units shown in formula I to form an admixture;
(b) forming the admixture into a shaped, solid article; and
(c) implanting or injecting the solid article in vivo at a preselected site, such that the solid, implanted or injected article is in at least partial contact with a biological fluid.
Polymers of the Invention
As used herein, the term xe2x80x9caliphaticxe2x80x9d refers to a linear, branched, or cyclic alkane, alkene, or alkyne. Preferred aliphatic groups in the poly(phosphonate) polymer of the invention are linear or branched alkanes having from 1 to 10 carbons, preferably being linear alkane groups of 1 to 7 carbon atoms.
As used herein, the term xe2x80x9caromaticxe2x80x9d refers to an unsaturated cyclic carbon compound with 4n+2 xcfx80 electrons.
As used herein, the term xe2x80x9cheterocyclicxe2x80x9d refers to a saturated or unsaturated ring compound having one or more atoms other than carbon in the ring, for example, nitrogen, oxygen or sulfur.
The biodegradable terephthalate block copolymer composition of the invention comprises the recurring monomeric units shown in formula I: 
wherein R is a divalent organic moiety. R can be any divalent organic moiety so long as it does not interfere with the polymerization, copolymerization, or biodegradation reactions of the copolymer. Specifically, R can be an aliphatic group, for example, alkylene, such as ethylene, 1,2-dimethylethylene, n-propylene, isopropylene, 2-methylpropylene, 2,2-dimethylpropylene or tert-butylene, tert-pentylene, n-hexylene, n-heptylene and the like; alkenylene, such as ethenylene, propenylene, dodecenylene, and the like; alkynylene, such as propynylene, hexynylene, octadecynylene, and the like; an aliphatic group substituted with a non-interfering substituent, for example, hydroxy-, halogen- or nitrogen-substituted aliphatic group; or a cycloaliphatic group such as cyclopentylene, 2-methylcyclopentylene, cyclohexylene, cyclohexenylene and the like.
R can also be a divalent aromatic group, such as phenylene, benzylene, naphthalene, phenanthrenylene, and the like, or a divalent aromatic group substituted with a non-interfering substituent. Further, R can also be a divalent heterocyclic group, such as pyrrolylene, furanylene, thiophenylene, alkylene-pyrrolylene-alkylene, pyridylene, pyridinylene, pyrimidinylene and the like, or may be any of these substituted with a non-interfering substituent.
Preferably, however, R is an alkylene group, a cycloaliphatic group, a phenylene group, or a divalent group having the formula: 
wherein Y is oxygen, nitrogen, or sulfur, and m is 1 to 3. More preferably, R is an alkylene group having from 1 to 7 carbon atoms and, most preferably, R is an ethylene group.
The value of x can vary depending on the desired solubility of the polymer, the desired Tg, the desired stability of the polymer, the desired stiffness of the final polymers, and the biodegradability and the release characteristics desired in the polymer. However, x generally is xe2x89xa71 and, typically, varies between 1 and 40. Preferably, x is from about 1 to about 30, more preferably, from about 1 to about 20 and, most preferably, from about 2 to about 20.
The most common way of controlling the value of x is to vary the feed ratio of the xe2x80x9cxxe2x80x9d portion relative to the monomer. For example, in the case of making the polymer: 
widely varying feed ratios of the dialkyl phosphite xe2x80x9cxxe2x80x9d reactant can be used with the diol reactant. Feed ratios of the reactants can easily vary from 99:1 to 1:99, for example, 95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, 50:50, 45:55, 20:80, 15:85, and the like. Preferably, the feed ratio between the dialkyl phosphite reactant and the diol reactant varies from about 90:10 to about 50:50; even more preferably, from about 85:15 to about 50:50; and most preferably, from about 80:20 to about 50:50.
The number n can vary greatly depending on the biodegradability and the release characteristics desired in the polymer, but typically varies from about 3 to 7,500, preferably between 5 and 5,000. More preferably, n is from about 5 to about 300 and most preferably, from about 5 to about 200.
The polymer of the invention can also comprise additional biocompatible monomeric units so long as they do not interfere with the biodegradable characteristics desired. Such additional monomeric units may offer even greater flexibility in designing the precise release profile desired for targeted drug delivery or the precise rate of biodegradability desired for structural implants. Examples of such additional biocompatible monomers include the recurring units found in polycarbonates; polyorthoesters; polyamides; polyurethanes; poly(iminocarbonates); and polyanhydrides.
Biodegradable polymers differ from non-biodegradable polymers in that they can be degraded during in vivo therapy. This generally involves breaking down the polymer into its monomeric subunits. In principle, the ultimate hydrolytic breakdown products of a poly(phosphite) are phosphite, alcohol, and diol, all of which are potentially non-toxic. The intermediate oligomeric products of the hydrolysis may have different properties, but the toxicology of a biodegradable polymer intended for implantation or injection, even one synthesized from apparently innocuous monomeric structures, is typically determined after one or more in vitro toxicity analyses.
The biodegradable polymer composition of the invention is preferably sufficiently pure to be biocompatible itself and remains biocompatible upon biodegradation. By xe2x80x9cbiocompatiblexe2x80x9d is meant that the biodegradation products or the polymer are non-toxic and result in only minimal tissue irritation when implanted or injected into vasculated tissue.
The polymer of the invention is preferably soluble in one or more common organic solvents for ease of fabrication and processing. Common organic solvents include such solvents as chloroform, dichloromethane, acetone, ethyl acetate, DMAC, N-methyl pyrrolidone, dimethylformamide, and dimethylsulfoxide. The polymer is preferably soluble in at least one of the above solvents.
The glass transition temperature (Tg) of the polymer of the invention can vary widely depending upon the branching of the diols used to prepare the polymer, the relative proportion of phosphorus-containing monomer used to make the polymer, and the like. However, preferably, the Tg is within the range of about xe2x88x9210xc2x0 C. to about 100xc2x0 C. and, even more preferably, between about 0 and 50xc2x0 C.
Non-Osteoconductivity of the Polymer
The polymers of the present invention are preferably non-osteoconductive. An osteoconductive material is one which facilitates bone growth in an area of the body where osseous growth, rather than soft tissue growth, would be expected.
An osteoconductive material generally acts as a scaffold into which bone filaments grow without the formation of separating fibrous tissue, as often occurs when objects are implanted into the body. For this reason, osteoconductive materials are often porous materials having a pore diameter of at least one-tenth of a millimeter (100 microns) in width to provide facilitation of tissue and bone growth.
One method of measuring the pore size and porosity of a material is to record the mercury intrusion volume into a material at different pressures with a Model 30K-A-1 Mercury Porosimeter (Porous Materials, Inc., Ithaca, N.Y.). The porosimeter analyzes a material to determine properties such as the pore surface area, total pore volume and mean pore size. The porosimeter is able to measure pores ranging in size from 35 Angstroms to 500 microns. The pore size is an important measurement to consider when determining whether a material is osteoconductive or not.
The polymer compositions and devices of the present invention are not osteoconductive and thus need not be porous. Preferably, they are non-porous, have pore diameters of less than 100 microns, or have only a very small number of pore diameters over 100 microns. In any event, the polymers of the invention do not promote bone growth and, accordingly, need not provide an adequate structure for supporting a network of bone filaments. Thus the polymers of the present invention are advantageously suited for controlled rates of biodegradation and concomitant release of biologically active materials.
Synthesis of Terephthalate-Poly(phosphite) Polymers
The most common general reaction in preparing a poly(phosphite) is a condensation of a diol with a dialkyl or diaryl phosphite according to the following equation: 
Poly(phosphites) can also be obtained by employing tetraalkyldiamides of phosphorous acid as condensing agents, according to the following equation: 
The above polymerization reactions can be either in bulk or solution polymerization. An advantage of bulk polycondensation is that it avoids the use of solvents and large amounts of other additives, thus making purification more straight-forward. It can also provide polymers of reasonably high molecular weight. Somewhat rigorous conditions, however, are often required and can lead to chain acidolysis (or hydrolysis if water is present). Unwanted, thermally-induced side reactions, such as cross-linking reactions, can also occur if the polymer backbone is susceptible to hydrogen atom abstraction or oxidation with subsequent macroradical recombination. To minimize these side reactions, the polymerization is preferably carried out in solution.
Solution polycondensation requires that both the diol and the phosphorus component be soluble in a common solvent. Typically, a chlorinated organic solvent is used, such as chloroform, dichloromethane, or dichloroethane. The solution polymerization is preferably run in the presence of equimolar amounts of the reactants and a stoichiometric amount of an acid acceptor, usually a tertiary amine such as pyridine or triethylamine. The product is then typically isolated from the solution by precipitation with a non-solvent and purified to remove the hydrochloride salt by conventional techniques known to those of ordinary skill in the art, such as by washing with an aqueous acidic solution, e.g., dilute HCl.
Reaction times tend to be longer with solution polymerization than with bulk polymerization. However, because overall milder reaction conditions can be used, side reactions are minimized, and more sensitive functional groups can be incorporated into the polymer. The disadvantages of solution polymerization are that the attainment of high molecular weights, such as a Mw greater than 20,000, is less likely.
Interfacial polycondensation can be used when high molecular weight polymers are desired at high reaction rates. Mild conditions minimize side reactions. Also the dependence of high molecular weight on stoichiometric equivalence between diol and phosphite inherent in solution methods is removed. However, hydrolysis of the acid chloride may occur in the alkaline aqueous phase. Phase transfer catalysts, such as crown ethers or tertiary ammonium chloride, can be used to bring the ionized diol to the interface to facilitate the polycondensation reaction. The yield and molecular weight of the resulting polymer after interfacial polycondensation are affected by reaction time, molar ratio of the monomers, volume ratio of the immiscible solvents, the type of acid acceptor, and the type and concentration of the phase transfer catalyst.
In a preferred embodiment of the invention, the biodegradable terephthalate polymer of formula I comprises the steps of polymerizing p moles of a diol compound having formula II: 
wherein R is as defined above, with q moles of a dialkyl or diaryl of formula III: 
wherein p greater than q, to form q moles of a homopolymer of formula IV, shown below: 
wherein R and x are as defined above. The homopolymer so formed can be isolated, purified and used as is. Alternatively, the homopolymer, isolated or not, can be used to prepare a block copolymer composition of the invention by:
(a) polymerizing as described above; and
(b) further reacting the homopolymer of formula IV and excess diol of formula II with (p-q) moles of terephthaloyl chloride having the formula V: 
xe2x80x83to form the copolymer of formula I.
The polymerization step (a) can take place at widely varying temperatures, depending upon the solvent used, the solubility desired, the molecular weight desired and the susceptibility of the reactants to form side reactions. Preferably, however, the polymerization step (a) takes place at a temperature from about xe2x88x9240 to about +160xc2x0 C. for solution polymerization, preferably from about 0 to 65xc2x0 C.; in bulk, temperatures in the range of about +150xc2x0 C. are generally used.
The time required for the polymerization step (a) also can vary widely, depending on the type of polymerization being used and the molecular weight desired. Preferably, however, the polymerization step (a) takes place during a time between about 30 minutes and 24 hours.
While the polymerization step (a) may be in bulk, in solution, by interfacial polycondensation, or any other convenient method of polymerization, preferably, the polymerization step (a) is a solution polymerization reaction. Particularly when solution polymerization reaction is used, an acid acceptor is advantageously present during the polymerization step (a). A particularly suitable class of acid acceptor comprises tertiary amines, such as pyridine, trimethylamine, triethylamine, substituted anilines and substituted aminopyridines. The most preferred acid acceptor is the substituted aminopyridine 4-dimethyl-aminopyridine (xe2x80x9cDMAPxe2x80x9d).
The addition sequence for the polymerization step (a) can vary significantly depending upon the relative reactivities of the diol of formula II, the dialkyl or diaryl phosphite of formula III, and the homopolymer of formula IV; the purity of these reactants; the temperature at which the polymerization reaction is performed; the degree of agitation used in the polymerization reaction; and the like. Preferably, however, the diol of formula II is combined with a solvent and an acid acceptor, and then the dialkyl or diaryl phosphite is added slowly. For example, a solution of the dialkyl or diaryl phosphite in a solvent may be trickled in or added dropwise to the chilled reaction mixture of diol, solvent and acid acceptor, to control the rate of the polymerization reaction.
The purpose of the copolymerization of step (b) is to form a block copolymer comprising (i) the phosphorylated homopolymer chains produced as a result of polymerization step (a) and (ii) interconnecting polyester units. The result is a block copolymer having a microcrystalline structure particularly well-suited to use as a controlled release medium.
The copolymerization step (b) of the invention usually takes place at a slightly higher temperature than the temperature of the polymerization step (a), but also may vary widely, depending upon the type of copolymerization reaction used, the presence of one or more catalysts, the molecular weight desired, the solubility desired, and the susceptibility of the reactants to undesirable side reaction. However, when the copolymerization step (b) is carried out as a solution polymerization reaction, it typically takes place at a temperature between about xe2x88x9240 and 100xc2x0 C. Typical solvents include methylene chloride, chloroform, or any of a wide variety of inert organic solvents.
The time required for the copolymerization of step (b) can also vary widely, depending on the molecular weight of the material desired and, in general, the need to use more or less rigorous conditions for the reaction to proceed to the desired degree of completion. Typically, however, the copolymerization step (b) takes place during a time of about 30 minutes to 24 hours.
When the polymer of the invention is synthesized by a two-step solution polycondensation to produce a block copolymer, the addition sequence of the reactive phosphites and the reaction temperatures in each step are preferably optimized to obtain the combination of molecular weight desired with good solubility in common organic solvents. Preferably, the additive sequence comprises dissolving the bis-terephthalate starting material with an acid acceptor in a solvent in which both are soluble, chilling the solution with stirring, slowly adding an equal molar amount of the dialkyl or diaryl phosphite (dissolved in the same solvent) to the solution, allowing the reaction to proceed at room temperature for a period of time, slowly adding an appropriate amount of terephthaloyl chloride, which is also dissolved in the same solvent, and increasing the temperature to about 50xc2x0 C. before refluxing overnight.
The polymer of formula I, whether a homopolymer or a block polymer, is isolated from the reaction mixture by conventional techniques, such as by precipitating out, extraction with an immiscible solvent, evaporation, filtration, crystallization and the like. Typically, however, the polymer of formula I is both isolated and purified by quenching a solution of said polymer with a non-solvent or a partial solvent, such as diethyl ether or petroleum ether.
Biodegradability and Release Characteristics
When working with poly(phosphates) and poly(phosphonates), the structure of the side chain can influence the release behavior of the polymer. For example, it is generally expected that, with these classes of poly(phosphoesters), conversion of the phosphorus side chain to a more lipophilic, more hydrophobic or bulky group would slow down the degradation process. For example, release would usually be faster from copolymer compositions with a small aliphatic group side chain than with a bulky aromatic side chain.
The terephthalate poly(phosphites) of formula I is usually characterized by a release rate of the biologically active substance in vivo that is controlled at least in part as a function of hydrolysis of the phosphoester bond of the polymer during biodegradation. However, poly(phosphites) do not have a side chain that can be manipulated to influence the rate of biodegradation.
Therefore, it has been somewhat surprising to discover that the lifetime of a biodegradable terephthalate poly(phosphite) polymer in vivo depends sufficiently upon its molecular weight, crystallinity, biostability, and the degree of cross-linking to still achieve acceptable degradation rates. In general, the greater the molecular weight, the higher the degree of crystallinity, and the greater the biostability, the slower biodegradation will be.
Biologically Active Substances
The polymer of formula I is preferably used as a non-osteoconductive, non-porous composition containing, in addition to the polymer, a biologically active substance to form a variety of useful biodegradable materials. The biologically active substance of the invention can vary widely with the purpose for the composition. The active substance(s) may be described as a single entity or a combination of entities. The delivery system is designed to be used with biologically active substances having high water-solubility as well as with those having low water-solubility to produce a delivery system that has controlled release rates. The term xe2x80x9cbiologically active substancexe2x80x9d includes, without limitation, medicaments; vitamins; mineral supplements; substances used for the treatment, prevention, diagnosis, cure or mitigation of disease or illness; or substances which affect the structure or function of the body; or pro-drugs, which become biologically active or more active after they have been placed in a predetermined physio-logical environment.
Non-limiting examples of broad categories of useful biologically active substances include the following expanded therapeutic categories: anabolic agents, antacids, anti-asthmatic agents, anticholesterolemic and anti-lipid agents, anti-coagulants, anti-convulsants, anti-diarrheals, anti-emetics, anti-infective agents, anti-inflammatory agents, anti-manic agents, anti-nauseants, anti-neoplastic agents, anti-obesity agents, anti-pyretic and analgesic agents, anti-spasmodic agents, anti-thrombotic agents, anti-uricemic agents, anti-anginal agents, antihistamines, anti-tussives, appetite suppressants, biologicals, cerebral dilators, coronary dilators, decongestants, diuretics, diagnostic agents, erythropoietic agents, expectorants, gastrointestinal sedatives, hyperglycemic agents, hypnotics, hypoglycemic agents, ion exchange resins, laxatives, mineral supplements, mucolytic agents, neuromuscular drugs, peripheral vasodilators, psychotropics, sedatives, stimulants, thyroid and anti-thyroid agents, uterine relaxants, vitamins, and pro-drugs.
Specific examples of useful biologically active substances from the above categories include: (a) anti-neoplastics such as androgen inhibitors, anti-metabolites, cytotoxic agents, and immuno-modulators; (b) anti-tussives such as dextromethorphan, dextromethorphan hydrobromide, noscapine, carbetapentane citrate, and chlophedianol hydrochloride; (c) antihistamines such as chlorpheniramine maleate, phenindamine tartrate, pyrilamine maleate, doxylamine succinate, and phenyltoloxamine citrate; (d) decongestants such as phenylephrine hydrochloride, phenylpropanolamine hydrochloride, pseudoephedrine hydrochloride, and ephedrine; (e) various alkaloids such as codeine phosphate, codeine sulfate and morphine; (f) mineral supplements such as potassium chloride, zinc chloride, calcium carbonates, magnesium oxide, and other alkali metal and alkaline earth metal salts; (g) ion exchange resins such as cholestryramine; (h) antiarrhythmics such as N-acetylprocainamide; (i) antipyretics and analgesics such as acetaminophen, aspirin and ibuprofen; (j) appetite suppressants such as phenylpropanolamine hydrochloride or caffeine; (k) expectorants such as guaifenesin; (l) antacids such as aluminum hydroxide and magnesium hydroxide; (m) biologicals such as peptides, polypeptides, proteins and amino acids, hormones, interferons or cytokines and other bioactive peptidic compounds, such as hGH, tPA, calcitonin, ANF, EPO and insulin; and (n) anti-infective agents such as antifungals, antivirals, antiseptics and antibiotics.
Non-limiting examples of useful biologically active substances include the following therapeutic categories: Analgesics, such as nonsteroidal anti-inflammatory drugs, opiate agonists and salicylates; antihistamines, such as H1-blockers and H2-blockers; anti-infective agents, such as anthelmintics, antianaerobics, antibiotics, aminoglycoside antibiotics, antifungal antibiotics, cephalosporin antibiotics, macrolide antibiotics, miscellaneous xcex2-lactam antibiotics, penicillin antibiotics, quinolone antibiotics, sulfonamide antibiotics, tetracycline antibiotics, antimycobacterials, antituberculosis antimycobacterials, antiprotozoals, antimalarial antiprotozoals, antiviral agents, anti-retroviral agents, scabicides, and urinary anti-infectives; antineoplastic agents, such as alkylating agents, nitrogen mustard alkylating agents, nitrosourea alkylating agents, antimetabolites, purine analog antimetabolites, pyrimidine analog antimetabolites, hormonal antineoplastics, natural antineoplastics, antibiotic natural antineoplastics, and vinca alkaloid natural antineoplastics; autonomic agents, such as anticholinergics, antimuscarinic anticholinergics, ergot alkaloids, parasympathomimetics, cholinergic agonist parasympathomimetics, cholinesterase inhibitor parasympathomimetics, sympatholytics, xcex1-blocker sympatholytics, xcex2-blocker sympatholytics, sympathomimetics, and adrenergic agonist sympathomimetics; cardiovascular agents, such as antianginals, xcex2-blocker antianginals, calcium-channel blocker antianginals, nitrate antianginals, antiarrhythmics, cardiac glycoside antiarrhythmics, class I antiarrhythmics, class II antiarrhythmics, class III antiarrhythmics, class IV antiarrhythmics, antihypertensive agents, xcex1-blocker antihypertensives, angiotensin-converting enzyme inhibitor (ACE inhibitor) antihypertensives, xcex2-blocker antihypertensives, calcium-channel blocker antihypertensives, central-acting adrenergic antihypertensives, diuretic anti-hypertensive agents, peripheral vasodilator anti-hypertensives, anti-lipemics, bile acid sequestrant anti-lipemics, HMG-COA reductase inhibitor anti-lipemics, inotropes, cardiac glycoside inotropes, and thrombolytic agents; dermatological agents, such as antihistamines, anti-inflammatory agents, corticosteroid anti-inflammatory agents, antipruritics/local anesthetics, topical anti-infectives, antifungal topical anti-infectives, antiviral topical anti-infectives, and topical antineoplastics; electrolytic and renal agents, such as acidifying agents, alkalinizing agents, diuretics, carbonic anhydrase inhibitor diuretics, loop diuretics, osmotic diuretics, potassium-sparing diuretics, thiazide diuretics, electrolyte replacements, and uricosuric agents; enzymes, such as pancreatic enzymes and thrombolytic enzymes; gastrointestinal agents, such as anti-diarrheals, antiemetics, gastrointestinal anti-inflammatory agents, salicylate gastrointestinal anti-inflammatory agents, antacid anti-ulcer agents, gastric acid-pump inhibitor anti-ulcer agents, gastric mucosal anti-ulcer agents, H2-blocker anti-ulcer agents, cholelitholytic agents, digestants, emetics, laxatives and stool softeners, and prokinetic agents; general anesthetics, such as inhalation anesthetics, halogenated inhalation anesthetics, intravenous anesthetics, barbiturate intravenous anesthetics, benzo-diazepine intravenous anesthetics, and opiate agonist intravenous anesthetics; hematological agents, such as antianemia agents, hematopoietic antianemia agents, coagulation agents, anticoagulants, hemostatic coagulation agents, platelet inhibitor coagulation agents, thrombolytic enzyme coagulation agents, and plasma volume expanders; hormones and hormone modifiers, such as abortifacients, adrenal agents, corticosteroid adrenal agents, androgens, anti-androgens, antidiabetic agents, sulfonylurea antidiabetic agents, antihypoglycemic agents, oral contraceptives, progestin contraceptives, estrogens, fertility agents, oxytocics, parathyroid agents, pituitary hormones, progestins, antithyroid agents, thyroid hormones, and tocolytics; immunobiologic agents, such as immunoglobulins, immunosuppressives, toxoids, and vaccines; local anesthetics, such as amide local anesthetics and ester local anesthetics; musculoskeletal agents, such as anti-gout anti-inflammatory agents, corticosteroid anti-inflammatory agents, gold compound anti-inflammatory agents, immunosuppressive anti-inflammatory agents, nonsteroidal anti-inflammatory drugs (NSAIDs), salicylate anti-inflammatory agents, skeletal muscle relaxants, neuromuscular blocker skeletal muscle relaxants, and reverse neuromuscular blocker skeletal muscle relaxants; neurological agents, such as anticonvulsants, barbiturate anticonvulsants, benzo-diazepine anticonvulsants, anti-migraine agents, anti-parkinsonian agents, anti-vertigo agents, opiate agonists, opiate antagonists, and PARP inhibitors; ophthalmic agents, such as anti-glaucoma agents, xcex2-blocker anti-glaucoma agents, miotic anti-glaucoma agents, mydriatics, adrenergic agonist mydriatics, antimuscarinic mydriatics, ophthalmic anesthetics, ophthalmic anti-infectives, ophthalmic aminoglycoside anti-infectives, ophthalmic macrolide anti-infectives, ophthalmic quinolone anti-infectives, ophthalmic sulfonamide anti-infectives, ophthalmic tetracycline anti-infectives, ophthalmic anti-inflammatory agents, ophthalmic corticosteroid anti-inflammatory agents, and ophthalmic nonsteroidal anti-inflammatory drugs (NSAIDs); psychotropic agents, such as antidepressants, heterocyclic antide-pressants, monoamine oxidase inhibitors (MAOIs), selective serotonin re-uptake inhibitors (SSRIs), tricyclic antidepressants, antimanics, antipsycho-tics, phenothiazine antipsychotics, anxiolytics, sedatives, and hypnotics, barbiturate sedatives and hypnotics, benzodiazepine anxiolytics, sedatives, and hypnotics, and psychostimulants; respiratory agents, such as antitussives, bronchodilators, adrenergic agonist bronchodilators, antimuscarinic broncho-dilators, expectorants, mucolytic agents, respiratory anti-inflammatory agents, and respiratory cortico-steroid anti-inflammatory agents; toxicology agents, such as antidotes, heavy metal antagonists/chelating agents, substance abuse agents, deterrent substance abuse agents, and withdrawal substance abuse agents; minerals; and vitamins, such as vitamin A, vitamin B, vitamin C, vitamin D, vitamin E, and vitamin K.
Preferred classes of useful biologically active substances from the above categories include: (1) nonsteroidal anti-inflammatory drugs (NSAIDs) analgesics, such as diclofenac, ibuprofen, ketoprofen, and naproxen; (2) opiate agonist analgesics, such as codeine, fentanyl, hydromorphone, and morphine; (3) salicylate analgesics, such as aspirin (ASA) (enteric coated ASA); (4) H1-blocker antihistamines, such as clemastine and terfenadine; (5) H2-blocker antihistamines, such as cimetidine, famotidine, nizadine, and ranitidine; (6) anti-infective agents, such as mupirocin; (7) antianaerobic anti-infectives, such as chloramphenicol and clindamycin; (8) antifungal antibiotic anti-infectives, such as amphotericin b, clotrimazole, fluconazole, and ketoconazole; (9) macrolide antibiotic anti-infectives, such as azithromycin and erythromycin; (10) miscellaneous xcex2-lactam antibiotic anti-infectives, such as aztreonam and imipenem; (11) penicillin antibiotic anti-infectives, such as nafcillin, oxacillin, penicillin G, and penicillin V; (12) quinolone antibiotic anti-infectives, such as ciprofloxacin and norfloxacin; (13) tetracycline 1antibiotic anti-infectives, such as doxycycline, minocycline, and tetracycline; (14) antituberculosis antimycobacterial anti-infectives such as isoniazid (INH), and rifampin; (15) antiprotozoal anti-infectives, such as atovaquone and dapsone; (16) antimalarial antiprotozoal anti-infectives, such as chloroquine and pyrimethamine; (17) anti-retroviral anti-infectives, such as ritonavir and zidovudine; (18) antiviral anti-infective agents, such as acyclovir, ganciclovir, interferon alfa, and rimantadine; (19) alkylating antineoplastic agents, such as carboplatin and cisplatin; (20) nitrosourea alkylating antineoplastic agents, such as carmustine (BCNU); (21) antimetabolite antineoplastic agents, such as methotrexate; (22) pyrimidine analog antimetabolite antineoplastic agents, such as fluorouracil (5-FU) and gemcitabine; (23) hormonal antineoplastics, such as goserelin, leuprolide, and tamoxifen; (24) natural antineoplastics, such as aldesleukin, interleukin-2, docetaxel, etoposide (VP-16), interferon alfa, paclitaxel, and tretinoin (ATRA); (25) antibiotic natural antineoplastics, such as bleomycin, dactinomycin, daunorubicin, doxorubicin, and mitomycin; (26) vinca alkaloid natural antineoplastics, such as vinblastine and vincristine; (27) autonomic agents, such as nicotine; (28) anticholinergic autonomic agents, such as benztropine and trihexyphenidyl; (29) antimuscarinic anticholinergic autonomic agents, such as atropine and oxybutynin; (30) ergot alkaloid autonomic agents, such as bromocriptine; (31) cholinergic agonist parasympathomimetics, such as pilocarpine; (32) cholinesterase inhibitor parasympathomimetics, such as pyridostigmine; (33) xcex1-blocker sympatholytics, such as prazosin; (34) xcex2-blocker sympatholytics, such as atenolol; (35) adrenergic agonist sympathomimetics, such as albuterol and dobutamine; (36) cardiovascular agents, such as aspirin (ASA) (enteric coated ASA); (37) xcex2-blocker antianginals, such as atenolol and propranolol; (38) calcium-channel blocker anti-anginals, such as nifedipine and verapamil; (39) nitrate antianginals, such as isosorbide dinitrate (ISDN); (40) cardiac glycoside antiarrhythmics, such as digoxin; (41) class I antiarrhythmics, such as lidocaine, mexiletine, phenytoin, procainamide, and quinidine; (42) class II antiarrhythmics, such as atenolol, metoprolol, propranolol, and timolol; (43) class III antiarrhythmics, such as amiodarone; (44) class IV antiarrhythmics, such as diltiazem and verapamil; (45) xcex1-blocker antihypertensives, such as prazosin; (46) angiotensin-converting enzyme inhibitor (ACE inhibitor) antihypertensives, such as captopril and enalapril; (47) xcex2-blocker antihypertensives, such as atenolol, metoprolol, nadolol, and propanolol; (48) calcium-channel blocker antihypertensive agents, such as diltiazem and nifedipine; (49) central-acting adrenergic antihyper-tensives, such as clonidine and methyldopa; (50) diuretic antihypertensive agents, such as amiloride, furosemide, hydrochlorothiazide (HCTZ), and spironolactone; (51) peripheral vasodilator antihypertensives, such as hydralazine and minoxidil; (52) anti-lipemics, such as gemfibrozil and probucol; (53) bile acid sequestrant anti-lipemics, such as cholestyramine; (54) HMG-COA reductase inhibitor anti-lipemics, such as lovastatin and pravastatin; (55) inotropes, such as amrinone, dobutamine, and dopamine; (56) cardiac glycoside inotropes, such as digoxin; (57) thrombolytic agents, such as alteplase (TPA), anistreplase, streptokinase, and urokinase; (58) dermatological agents, such as colchicine, isotretinoin, methotrexate, minoxidil, tretinoin (ATRA); (59) dermatological corticosteroid anti-inflammatory agents, such as betamethasone and dexamethasone; (60) anti-fungal topical anti-infectives, such as amphotericin B, clotrimazole, miconazole, and nystatin; (61) antiviral topical anti-infectives, such as acyclovir; (62) topical antineoplastics, such as fluorouracil (5-FU); (63) electrolytic and renal agents, such as lactulose; (64) loop diuretics, such as furosemide; (65) potassium-sparing diuretics, such as triamterene; (66) thiazide diuretics, such as hydrochlorothiazide (HCTZ); (67) uricosuric agents, such as probenecid; (68) enzymes such as RNase and DNase; (69) thrombolytic enzymes, such as alteplase, anistreplase, streptokinase and urokinase; (70) antiemetics, such as prochlorperazine; (71) salicylate gastrointestinal anti-inflammatory agents, such as sulfasalazine; (72) gastric acid-pump inhibitor anti-ulcer agents, such as omeprazole; (73) H2-blocker anti-ulcer agents, such as cimetidine, famotidine, nizatidine, and ranitidine; (74) digestants, such as pancrelipase; (75) prokinetic agents, such as erythromycin; (76) opiate agonist intravenous anesthetics such as fentanyl; (77) hematopoietic antianemia agents, such as erythropoietin, filgrastim (G-CSF), and sargramostim (GM-CSF); (78) coagulation agents, such as antihemophilic factors 1-10 (AHF 1-10); (79) anticoagulants, such as warfarin; (80) thrombolytic enzyme coagulation agents, such as alteplase, anistreplase, streptokinase and urokinase; (81) hormones and hormone modifiers, such as bromocriptine; (82) abortifacients, such as methotrexate; (83) anti-diabetic agents, such as insulin; (84) oral contraceptives, such as estrogen and progestin; (85) progestin contraceptives, such as levonorgestrel and norgestrel; (86) estrogens such as conjugated estrogens, diethylstilbestrol (DES), estrogen (estradiol, estrone, and estropipate); (87) fertility agents, such as clomiphene, human chorionic gonadotropin (HCG), and menotropins; (88) parathyroid agents such as calcitonin; (89) pituitary hormones, such as desmopressin, goserelin, oxytocin, and vasopressin (ADH); (90) progestins, such as medroxyprogesterone, norethindrone, and progesterone; (91) thyroid hormones, such as levothyroxine; (92) immunobiologic agents, such as interferon beta-1b and interferon gamma-1b; (93) immunoglobulins, such as immune globulin IM, IMIG, IGIM and immune globulin IV, IVIG, IGIV; (94) amide local anesthetics, such as lidocaine; (95) ester local anesthetics, such as benzocaine and procaine; (96) musculoskeletal corticosteroid anti-inflammatory agents, such as beclomethasone, betamethasone, cortisone, dexamethasone, hydrocortisone, and prednisone; (97) musculoskeletal anti-inflammatory immunosuppressives, such as azathioprine, cyclophosphamide, and methotrexate; (98) musculoskeletal nonsteroidal anti-inflammatory drugs (NSAIDs), such as diclofenac, ibuprofen, ketoprofen, ketorlac, and naproxen; (99) skeletal muscle relaxants, such as baclofen, cyclobenzaprine, and diazepam; (100) reverse neuromuscular blocker skeletal muscle relaxants, such as pyridostigmine; (101) neurological agents, such as nimodipine, riluzole, tacrine and ticlopidine; (102) anticonvulsants, such as carbamazepine, gabapentin, lamotrigine, phenytoin, and valproic acid; (103) barbiturate anticonvulsants, such as phenobarbital and primidone; (104) benzodiazepine anticonvulsants, such as clonazepam, diazepam, and lorazepam; (105) anti-parkinsonian agents, such as bromocriptine, levodopa, carbidopa, and pergolide; (106) anti-vertigo agents, such as meclizine; (107) opiate agonists, such as codeine, fentanyl, hydromorphone, methadone, and morphine; (108) opiate antagonists, such as naloxone; (109) xcex2-blocker anti-glaucoma agents, such as timolol; (110) miotic anti-glaucoma agents, such as pilocarpine; (111) ophthalmic aminoglycoside anti-infectives, such as gentamicin, neomycin, and tobramycin; (112) ophthalmic quinolone anti-infectives, such as ciprofloxacin, norfloxacin, and ofloxacin; (113) ophthalmic corticosteroid anti-inflammatory agents, such as dexamethasone and prednisolone; (114) ophthalmic nonsteroidal anti-inflammatory drugs (NSAIDs), such as diclofenac; (115) antipsychotics, such as clozapine, haloperidol, and risperidone; (116) benzodiazepine anxiolytics, sedatives and hypnotics, such as clonazepam, diazepam, lorazepam, oxazepam, and prazepam; (117) psycho-stimulants, such as methylphenidate and pemoline; (118) antitussives, such as codeine; (119) bronchodilators, such as theophylline; (120) adrenergic agonist broncho-dilators, such as albuterol; (121) respiratory corticosteroid anti-inflammatory agents, such as dexamethasone; (122) antidotes, such as flumazenil and naloxone; (123) heavy metal antagonists/chelating agents, such as penicillamine; (124) deterrent substance abuse agents, such as disulfiram, naltrexone, and nicotine; (125) withdrawal substance abuse agents, such as bromocriptine; (126) minerals, such as iron, calcium, and magnesium; (127) vitamin B compounds, such as cyano-cobalamin (vitamin B12) and niacin (vitamin B3); (128) vitamin C compounds, such as ascorbic acid; and (129) vitamin D compounds, such as calcitriol.
In addition to the foregoing, the following less common drugs may also be used: Chlorhexidine, estradiol cypionate in oil, estradiol valerate in oil, flurbiprofen, flurbiprofen sodium, ivermectin, levodopa, nafarelin, and somatropin.
Further, the following new drugs may also be used: Recombinant beta-glucan; bovine immunoglobulin concentrate; bovine superoxide dismutase; a mixture comprising fluorouracil, epinephrine, and bovine collagen; recombinant hirudin (r-Hir), HIV-1 immunogen; human anti-TAC antibody; recombinant human growth hormone (r-hGH); recombinant human hemoglobin (r-Hb); recombinant human mecasermin (r-IGF-1); recombinant interferon beta-1a; lenograstim (G-CSF); olanzapine; recombinant thyroid stimulating hormone (r-TSH); and topotecan.
Further still, the following intravenous products may be used: acyclovir sodium, aldesleukin, atenolol, bleomycin sulfate, human calcitonin, salmon calcitonin, carboplatin, carmustine, dactinomycin, daunorubicin HCl, docetaxel, doxorubicin HCl, epoetin alfa, etoposide (VP-16), fluorouracil (5-FU), ganciclovir sodium, gentamicin sulfate, interferon alfa, leuprolide acetate, meperidine HCl, methadone HCl, methotrexate sodium, paclitaxel, ranitidine HCl, vinblastin sulfate, and zidovudine (AZT).
Still further, the following listing of peptides, proteins, and other large molecules may also be used, such as interleukins 1 through 18, including mutants and analogues; interferons xcex1, xcex2, and xcex3; luteinizing hormone releasing hormone (LHRH) and analogues, gonadotropin releasing hormone (GnRH), and transforming growth factor-xcex2 (TGF-xcex2); fibroblast growth factor (FGF); tumor necrosis factor-xcex1 and xcex2 (TNF-xcex1 and xcex2); nerve growth factor (NGF); growth hormone releasing factor (GHRF); epidermal growth factor (EGF); fibroblast growth factor homologous factor (FGFHF); hepatocyte growth factor (HGF); insulin growth factor (IGF); invasion inhibiting factor-2 (IIF-2); somatostatin; thymosin-xcex1-1; xcex3-globulin; superoxide dismutase (SOD); and complement factors.
Preferably, the biologically active substance is selected from the group consisting of peptides, polypeptides, proteins, amino acids, polysaccharides, growth factors, hormones, anti-angiogenesis factors, interferons or cytokines, and pro-drugs. In a particularly preferred embodiment, the biologically active substance is a therapeutic drug or pro-drug, most preferably a drug selected from the group consisting of chemotherapeutic agents and other antineoplastics (such as paclitaxel), antibiotics, anti-virals, anti-fungals, anti-inflammatories, anticoagulants, and pro-drugs of these substances.
The biologically active substances are used in amounts that are therapeutically effective. While the effective amount of a biologically active substance will depend on the particular material being used, amounts of the biologically active substance from about 1% to about 65% have been easily incorporated into the present delivery systems while achieving controlled release. Lesser amounts may be used to achieve efficacious levels of treatment for certain biologically active substances.
Pharmaceutically acceptable carriers may be prepared from a wide range of materials. Without being limited thereto, such materials include diluents, binders and adhesives, lubricants, disintegrants, colorants, bulking agents, flavorings, sweeteners and miscellaneous materials such as buffers and adsorbents in order to prepare a particular medicated composition.
Implants and Delivery Systems Designed for Injection
The composition can be used in an essentially non-osteoconductive medical device in the form of a biosorbable suture, a laminate for degradable or non-degradable fabrics, or a coating for an implantable device. In its simplest form, a biodegradable delivery system for a biologically active substance consists of a physical dispersion of the therapeutic agent in a polymer matrix. The therapeutic agent is typically released as the polymeric matrix biodegrades in vivo into soluble products that can be absorbed by and eventually excreted from the body.
In a particularly preferred embodiment, the essentially non-osteoconductive biodegradable composition of the invention is used to make an article useful for implantation, injection, or otherwise being placed totally or partially within the body. The biologically active substance of the composition and the polymer of the invention may form a homogeneous matrix, or the biologically active substance may be encapsulated in some way within the polymer. For example, the biologically active substance may be first encapsulated in a microsphere and then combined with the polymer in such a way that at least a portion of the microsphere structure is maintained.
Alternatively, the biologically active substance may be sufficiently immiscible in the polymer of the invention that it is dispersed as small droplets, rather than being dissolved, in the polymer. Either form is acceptable, but it is preferred that, regardless of the homogeneity of the composition, the release rate of the biologically active substance in vivo remain controlled, at least partially as a function of hydrolysis of the phosphoester bond of the polymer upon biodegradation.
In a preferred embodiment, the article of the invention is adapted for implantation or injection into the body of an animal. It is particularly important that such an article result in minimal tissue irritation when implanted or injected into vasculated tissue.
As all or part of an essentially non-osteoconductive, medical device, the copolymer compositions of the invention provide a physical form having specific chemical, physical, and mechanical properties sufficient for the application and a composition that degrades in vivo into non-toxic residues. Typical structural medical articles include such implants as ventricular shunts, laminates for degradable or nondegradable fabrics, drug-carriers, biosorbable sutures, burn dressings, coatings to be placed on other implant devices, and the like.
In vascular graft applications, a biodegradable material in the form of woven fabric can be used to promote tissue ingrowth. The copolymer composition of the invention may be used as a temporary barrier for preventing tissue adhesion, e.g., following abdominal surgery.
On the other hand, in nerve regeneration articles, the presence of a biodegradable supporting matrix can be used to facilitate cell adhesion and proliferation. When the copolymer composition is fabricated as a tube for nerve generation, for example, the tubular article can also serve as a geometric guide for axonal elongation in the direction of functional recovery.
As a drug delivery device, the copolymer composition of the invention provides a polymeric matrix capable of sequestering a biologically active substance and provides predictable, controlled delivery of the substance. The polymeric matrix then degrades to non-toxic residues.
Biodegradable medical implant devices and drug delivery products can be prepared in several ways. The copolymer can be melt processed using conventional extrusion or injection molding techniques, or these products can be prepared by dissolving in an appropriate solvent, followed by formation of the device, and subsequent removal of the solvent by evaporation or extraction. By these methods, the polymers may be formed into drug delivery systems of almost any size or shape desired, for example, implantable solid discs or wafers or injectable rods, microspheres, or other microparticles. Once a medical implant article is in place, it should remain in at least partial contact with a biological fluid, such as blood, internal organ secretions, mucous membranes, cerebrospinal fluid and the like.
The following examples are illustrative of preferred embodiments of the invention and are not to be construed as limiting the invention thereto. All polymer molecular weights are average molecular weights. All percentages are based on the percent by weight of the final delivery system or formulation being prepared, unless otherwise indicated, and all totals equal 100% by weight.